1. Field of the Invention
The present invention relates to a method of controlling the shape of iron or nonferrous metals strip and an apparatus therefor.
Herein, the strip shape designates a surface shape of strip such as a center buckle (the state where the central portion of the strip in the width direction thereof is stretched longer than the side edge portion thereof) and a wavy edge (the state wherein the side edge portion of the plate in the width direction thereof is stretched longer than the central portion thereof), in particular a strip shape appearing in the width direction of the strip. Since the strip is subjected to a tension by means of a rolling-mill and pinch-rolls in the rolling process, the strip shape does not appear according to circumstances. The shape corresponds to a tensile stress given to each portion of the strip in the width direction thereof in the rolling process. That is to say, the portion, on which a larger tensile stress is given, corresponds to the portion of which elongation is small, and v.v., and the shape is determined depending on such an elongation. Accordingly, means for measuring the shape, in short, a shape meter is constructed to measure a tensile stress at a large number of points of the strip being rolled in the width direction thereof.
2. Prior Art
The shape is remarkably important for the evaluation of the quality of the strip. A rolling mill, which is capable of controlling the strip shape, is disclosed in U.S. Pat. No. 4,269,051 (Clark et al.). This rolling mill is provided with a detector for detecting the tension, in short, abovementioned tensile stress downstream thereof and a signal obtained by the detector is used for controlling the strip shape. Summarizing Clark et al.'s invention in order to make the comparison of the invention with the present invention easy, the shape is approximated by a+bx+cx.sup.2 on the basis of an output signal from the detector, wherein x is a variable designating a distance from the center of the strip in the width direction thereof; a, b and c is a constant, respectively.
Although it is desired that the strip shape is flat, but the aimed strip shape which is desired in the rolling process is not flat, in short, it is not expressed by only the constant a excepting bx and cx.sup.2 in the above described formula. It is the reason of the above described that an influence of heat is given to the strip in the rolling process, the strip shape being detected by the tensile stress, and the tensile stress being different at end portions and the central portion of the strip in the width direction thereof even though the strip shape is identical. So, the shape aimed in the rolling process is expressed by a parabolical equation of x, and right and left pressing-down balancers for adjusting the leveling of roll gap, a roll-bender and a roll-cooling apparatus are controlled to coincide a quadratic equation (a+b+cx.sup.2) of the measured shape with the parabolical equation of the aimed shape. That is to say, according to Clark et al.'s invention, a term of the first power of x is controlled by the right and left pressing-down balancer and a quadratic term of x is controlled by the roll-bender and the roll-cooling apparatus.
In short, a rolling mill according to Clark et al.'s invention is ineffective for a complex shape defect appearing by compounding various forms of stretch at all. It is perhaps the reason of the above described that a parabolical equation approximating the strip shape is insufficient, the control of the strip shape by the roll-cooling apparatus being slow in response, whereby being ineffective for the control of the complex shape defect, and the like. In addition, since the strip shape is greatly dependent upon the control by said roll-cooling apparatus and the control of the shape by the roll-cooling apparatus is slow in response, it can not be said that the controlling accuracy is high even for a simple stretch. Furthermore, since it is necessary to stabilize a temperature of mill rolls to some extent, such disadvantages as the necessity of a warming up rolling are found.